This invention relates to an articulated joint construction for an industrial robot.
FIG. 1 shows a joint construction of this type known to the inventor, wherein a lower arm 2 is pivotally coupled to an upper arm 1 via a shaft 11 rigid with the lower arm. The rotational driving force is supplied by a motor 5 mounted to the upper arm and whose output shaft is keyed at 7 to a harmonic drive 6 of the type described in U.S. Pat. No. 4,096,766. The lower, output end of the harmonic drive rotates at a much slower speed than that of the motor 5, and is fixedly coupled to an upper end of the shaft 11 above its journal in a bearing 8. Reference numeral 9 designates a stopper ring, and 10 is a spacer sleeve. A flexible cable 3 carrying power lines, detection and control signal lines, pneumatic and/or hydraulic lines, etc. is threaded through the interiors of the upper and lower arms, and is bypassed around the articulation joint in a bight via sealing bushes 4 of rubber or the like.
A disadvantage of such construction resides in the externally exposed bight of the cable 3, which is prone to becoming caught by or hung up on portions of the workpiece and/or adjacent equipment, and which can thus become ruptured or severed and thereby create a serious industrial hazard.
In another known construction as described in Japanese kokai No. 62-48485 the cable 3 is threaded through the interior of the joint and is thus not externally exposed. With this construction the drive motor is disposed within one of the robot arms remote from the joint axis, however, and a power transmission mechanism including gears, belts or the like must thus be provided. This complicates the overall construction and attendantly increases the cost thereof, and further results in the generation of considerable dust and other contaminants due to the numerous moving parts required, which renders such an arrangement unacceptable for the use in a "clean" robotics environment such as an electronics components fabrication or assembly installation.